1. Field of the Invention
The present invention relates to a method of forming a magnetic pole section of a perpendicular magnetic recording type thin-film magnetic head and a method of manufacturing a perpendicular magnetic recording type thin-film magnetic head.
2. Description of the Related Art
With the increase in the recording densities of magnetic recording media such as hard disks, a shift is occurring from horizontal magnetic recording to perpendicular magnetic recording. Perpendicular magnetic recording has advantages that it provides higher linear recording density and makes recorded magnetic recording media less susceptible to thermal fluctuations.
A perpendicular magnetic recording type thin-film magnetic head includes a thin-film coil which generates a write field and a magnetic pole which extends backward from an air bearing surface (ABS) and guides a perpendicular magnetic field to a magnetic recording medium. The width of the trailing edge (trailing edge width) of a magnetic pole of the perpendicular magnetic recording type thin-film magnetic head that defines the recording track-width needs to be made as small as possible to cope with increasing surface recording densities.
US 2007/0195457A1 discloses a method of manufacturing a perpendicular magnetic recording type thin-film magnetic head that can reduce the trailing edge width. In the method, a resist pattern having an opening is formed, a nonmagnetic layer is formed so as to narrow the opening by covering an inner wall of the resist pattern, a magnetic layer is formed on the nonmagnetic layer in the opening, and then the surface is polished until the resist pattern is exposed to form a pattern of a main pole.
U.S. Pat. No. 5,075,956A and U.S. Pat. No. 6,954,340B disclose techniques which improve recording density by providing a shield (wrap around shield) that has an edge disposed to surround an edge of a main pole on the surface that faces a magnetic recording medium.
A nonmagnetic layer forms a gap between the wrap around shield and the main pole. The wrap around shield has the function of intercepting a magnetic flux that is generated from the edge of the main pole disposed on the surface facing the magnetic recording medium and extends in directions except the direction perpendicular to the surface facing the magnetic recording medium, thereby preventing the magnetic flux from reaching the magnetic recording medium. The wrap around shield includes a lower shield disposed on the air inflow end side of the slider with respect to the main pole, an upper shield disposed on the air outflow end side of the slider with respect to the main pole, and first and second side shields disposed on both sides of the main pole in the track-width direction. The gap includes a lower gap positioned between the main pole and the lower shield, an upper gap positioned between the main pole and the upper shield, and two side gaps positioned between the main pole and the two side shields. According to the technique, magnetic field gradient can be increased by the upper and lower shields and adjacent track erasing can be suppressed by the two side shields. These effects can increase the recording density.
A method of forming the side shields among the wrap around shields will be discussed below.
FIGS. 1a to 1d are cross-sectional views of side shields viewed from the ABS for explaining a conventional side shield forming method. FIGS. 2a and 2b are cross-sectional views of the side shields viewed from the ABS for explaining a problem with the method.
First, a pattern of a main pole is formed by the method disclosed in US 2007/0195157A1 and then the resist pattern is removed. The result is illustrated in FIG. 1a. Specifically, depicted in FIG. 1a are a main pole 10 formed, a nonmagnetic layer 11 of alumina (Al2O3), for example, formed on the side surfaces of the main pole 10, a nonmagnetic layer 12 of alumina formed under the main pole 10, and an under layer 13 of a nonmagnetic material such as alumina. In FIG. 1a, the distance between the bottom end of the main pole layer 10 and the top surface of the under layer 13, that is, the thickness of the nonmagnetic layer 12, is denoted by h1.
Then, etching is performed with an alkaline solution to remove the nonmagnetic layer 11. In this case, by the etching, the nonmagnetic layer 12 formed under the main pole 10 is removed and a portion of the under layer 13 is removed to produce an under layer 13′ with a reduced thickness as illustrated in FIG. 1b. In FIG. 1b, h2 denotes the thickness of the removed portion of the under layer 13.
Then, alumina is deposited by chemical vapor deposition (CVD) to form a nonmagnetic side shield gap layer 14 on the side surfaces of the main pole 10. By the deposition, a nonmagnetic layer 15 of alumina is also deposited below the main pole 10 as well as on the side surfaces of the main pole 10 as depicted in FIG. 1c. In FIG. 1c, the thickness of the side shield gap layer 14 or the nonmagnetic layer 15 is denoted by a.
Then, the top surface is plated with a magnetic material to form a side shield layer 16 as depicted in FIG. 1d. 
In the conventional side shield forming method as described above, if the thickness of the nonmagnetic layer 11 is increased in order to reduce the width of the main pole 10 in the track-width direction, the thickness h1 of the nonmagnetic layer 12 is also increased. Accordingly, the amount of etching by the alkaline solution for removing the nonmagnetic layers 11 and 12 also increases and therefore the depth to which the under layer 13 is removed increases, that is, h2 increases.
In this case, if the thickness a of the side shield gap layer 14 subsequently formed on the side surfaces of the main pole 10 is sufficiently large, that is, if 2a>h1+h2, the nonmagnetic layers 14 and 15 under the main pole 10 will be continuous as depicted in FIG. 2a after the alkaline etching and therefore a problem which will be described later does not arise. However, if the thickness a of the side shield gap layer 14 is small, that is, if 2a<h1+h2, the nonmagnetic layers 14′ and 15′ under the main pole 10 will be discontinuous and separated to form space in the region after the alkaline etching. Consequently, an unwanted lower shield layer will be formed in such space in the subsequent shield layer formation process. That is, the shape of the side shield layer will be distorted (deformation).